Thanks for the information. I was told that this model could be done in a single Harmonic Acoustics system, so I figured out how to add Physics Regions to make that happen. Once a Structural Physics Region is in the model, the FSI is automatically taken care of. I created a stand alone system to reproduce your result. The tabular data is correct, but the Frequency axis on the Worksheet is wrong.
Your model has the ports are at each end of the tube, a long way from where the incident and transmitted power is supposed to be measured at the plate . Since this is a lossless model, I suppose the power doesn't change along the tube, but I don't know why I can't use the face of the plate or the face of the air at the plate as a port. Can you explain that?